The present invention relates to a method and an apparatus for alarming decrease in tire air-pressure and a program for judging decompression of a tire. More particularly, it relates to a method and an apparatus for alarming decrease in tire air-pressure and a program for judging decompression of a tire with which it is possible to improve performance and safety of a vehicle upon detecting decrease in tire air-pressure on the basis of rotational information of the tires.
Conventionally, apparatuses for issuing an alarm upon detecting decrease in air-pressure of tires of a four-wheeled vehicle might be roughly divided into two methods, namely a direct detection method and an indirect method. The direct detection method is a method of directly measuring an internal pressure of tires upon incorporating air-pressure sensors in, for instance, tire valves (reference should be made to, for instance, Japanese Unexamined Patent Publication No. 139117/1999) while the indirect method is a method in which decrease in internal pressure is detected on the basis of relative differences between wheel speeds or rotational angular velocities which can be obtained from rotational information of tires (reference should be made to, for instance, Japanese Unexamined Patent Publication No. 305011/1988).
While the direct detection method is advantaged in that the absolute internal pressure of each of the four wheels can be detected, it is disadvantaged in that costs involved are extremely high since it is necessary to provide pressure sensors, transmitters and receivers. In contrast thereto, the indirect method is advantaged in that costs are low.
However, since decrease in internal pressure is detected in the indirect method upon relative comparison of wheel speeds of tires or similar, it is impossible to detect decrease in internal pressure when all four wheel tires have simultaneously decompressed in a natural manner. It is also impossible to detect simultaneous decompression of both wheel tires of driving wheels.
It is an object of the present invention to provide a method and an apparatus for alarming decrease in tire air-pressure and a program for judging decompression of a tire with which it is possible to detect decrease in tire air-pressure of at least the driving wheel tires by using an indirect method employing rotational information of the tires.
In accordance with a first aspect of the present invention, there is provided a method for alarming decrease in tire air-pressure, which alarms decrease in internal pressure of a tire on the basis of rotational information obtained from tires attached to a vehicle, the method including the steps of: detecting rotational information of respective tires; respectively calculating and storing a wheel speed, a vehicle acceleration, a slip ratio between front and rear wheels, a running distance and a turning radius on the basis of the rotational information of the respective tires; performing moving-averaging of the vehicle acceleration and the slip ratio between front and rear wheels; accumulating the running distance, the moving-averaged vehicle acceleration and the slip ratio between front and rear wheels when the turning radius is not less than a specified value; obtaining a linear regression coefficient and a correlation coefficient of the vehicle acceleration and the slip ratio between front and rear wheels when the accumulated running distance has reached a specified distance; judging whether at least a driving wheel tire has decompressed upon comparing a judged value of the linear regression coefficient and a reference value for internal pressure of the linear regression coefficient which has been preliminarily calculated in the above step when the tires are reference internal pressure, the linear regression coefficient when the correlation coefficient is not less than a specified value being set as the judged value; and issuing an alarm of decrease in tire air-pressure on the basis of the result of judgment of decompression.
In accordance with a second aspect of the present invention, there is further provided an apparatus for alarming decrease in tire air-pressure, including: rotational information detecting means which detects rotational information of respective tires; a first calculating means which respectively calculates and stores a wheel speed, a vehicle acceleration, a slip ratio between front and rear wheels, a running distance and a turning radius on the basis of the rotational information of the respective tires; a second calculating means which performs moving-averaging of the vehicle acceleration and the slip ratio between front and rear wheels; an accumulating means which accumulates the running distance, the moving-averaged vehicle acceleration and the slip ratio between front and rear wheels when the turning radius is not less than a specified value; a third calculating means which obtains a linear regression coefficient and a correlation coefficient of the vehicle acceleration and the slip ratio between front and rear wheels when the accumulated running distance has reached a specified distance; a decompression judging means which judges whether at least a driving wheel tire has decompressed upon comparing a judged value of the linear regression coefficient and a reference value for internal pressure of the linear regression coefficient which has been preliminarily calculated when the tires are reference internal pressure, the linear regression coefficient when the correlation coefficient is not less than a specified value being set as the judged value; and an alarming means which issues an alarm of decrease in tire air-pressure on the basis of the result of judgment of decompression.
In accordance with a third aspect of the present invention, there is still provided a program for judging decompression of a tire, wherein a computer is made to function, for judging decrease in tire air-pressure, as a first calculating means which respectively calculates and stores a wheel speed, a vehicle acceleration, a slip ratio between front and rear wheels, a running distance and a turning radius on the basis of the rotational information of the respective tires; a second calculating means which performs moving-averaging of the vehicle acceleration and the slip ratio between front and rear wheels; an accumulating means which accumulates the running distance, the moving-averaged vehicle acceleration and the slip ratio between front and rear wheels when the turning radius is not less than a specified value; a third calculating means which obtains a linear regression coefficient and a correlation coefficient of the vehicle acceleration and the slip ratio between front and rear wheels when the accumulated running distance has reached a specified distance; and a decompression judging means which judges whether at least a driving wheel tire has decompressed upon comparing a judged value of the linear regression coefficient and a reference value for internal pressure of the linear regression coefficient which has been preliminarily calculated when the tires are of reference internal pressure, the linear regression coefficient when the correlation coefficient is not less than a specified value being set as the judged value.